1. Field
The exemplary embodiments relate to a photon pair generator and a quantum cryptography system employing the same.
2. Description of the Related Art
Recently, as wired/wireless communication technology has rapidly advanced and various communication services have come into widespread use, security for communication networks has arisen as a very important issue. In particular, the importance of security for communication networks has increased more and more for protection of secrets related to countries, companies, and finance and personal information. Quantum cryptography has recently drawn much attention as a security solution for communication. Quantum cryptography is a communication security technology whereby security is guaranteed based on the principles of quantum mechanics that are basic rules of nature, thereby preventing wiretapping or monitoring. That is, quantum cryptography is technology whereby a secret key that may be used to encrypt and decrypt data to be exchanged between a transmitting side and a receiving side is distributed in an absolutely secure manner based on the laws of quantum physics such as the no-cloning theorem. Quantum cryptography has been also known as quantum key distribution (QKD) technology.
Representative examples of quantum cryptography or a quantum key distribution method include the BB84 protocol, B92 protocol, EPR protocol, etc. Many quantum cryptography protocols including the BB84 protocol employ a method of using a single-photon state. An ideal single-photon state refers to a state in which only one photon is present in a predetermined mode. The ideal single-photon state cannot be perfectly realized using current technology.
Recently, in the field of quantum information technology, not only the method using the single-photon state but also a method of using a quantum-entangled state in quantum cryptography communication has been frequently used. Since bulky three-dimensional (3D) nonlinear crystals have been mainly used to produce the quantum-entangled state, the quantum-entangled state is difficult to apply to small-sized integrated photonic chips.